The tabs may be cut out from a metal foil to form a web which is then folded round the edges of the package to extend underneath it. This is commonly the case for integrated circuits which are encapsulated in plastic or ceramic packages. Alternatively, the tabs may be deposited on the package by silk screen printing or by vacuum or electrolytic metalization, as is the case for so-called "chip carrier" type ceramic micropackages. In either case, the present invention is only applicable to packages in which the body material of the package is not wettable by solder (and in particular the invention is thus generally not applicable to metal-bodied packages). The invention is also not applicable to packages from which the connection tabs project in the form of pins suitable for being received in holes in a substrate. Such packages include many discrete components such as transistors, and also integrated circuits in DIL packages, for example.
Fixing such a pin-less package on an electric circuit substrate is difficult because of the accuracy required by the very small size of the tabs and by their close proximity to one another, together with the lack of positive location of the kind that pins could provide. Such a package must initially be held in place by having its body glued to the substrate, and then the connections are soldered by melting a layer of solder which has previously been deposited on the conductive tracks. Unfortunately, there is a conflict between the requirement that the package be held in place by glue prior to soldering, and the need for the package to move slightly to bring its tabs into direct contact with the tracks on the substrate when the solder melts. Further, the solder is not always evenly deposited with uniform thickness which can result in some adjacent pairs of contacts being short circuited while others are left open circuit since they are supported on either side by solder deposits of excessive thickness.
Preferred embodiments of the present invention mitigate the drawbacks outlined above.